Corrosion behavior of select MAX phases in NaOH, HCl and H2SO4

In this paper we report on the electrochemical corrosion of select MAX phases, namely Ti2AlC, (Ti,Nb)2AlC, V2AlC, V2GeC, Cr2AlC, Ti2AlN, Ti4AlN3, Ti3SiC2 and Ti3GeC2 in 1 M NaOH, 1 M HCl and 1 M H2SO4 solutions. Polarization characteristics recorded in 1 M NaOH show that V2AlC, V2GeC and Cr2AlC undergo active dissolution at potentials more positive than the corrosion potential, while Ti2AlC, (Ti,Nb)2AlC, Ti3SiC2 and Ti3GeC2 passivate. In the 1 M HCl solutions, Ti2AlC, V2AlC and V2GeC actively dissolve; Ti3SiC2 and Ti3GeC2 passivate. Depending on potential, (Ti,Nb)2AlC and Cr2AlC showed trans-passive behavior. In 1 M H2SO4 solutions, Ti2AlC, (Ti,Nb)2AlC, Ti3SiC2 and Ti3GeC2 passivate, V2AlC and V2GeC show active dissolution, while Cr2AlC exhibits trans-passive behavior. Ti2AlN and Ti4AlN3 were passive in all solutions except in 1 M HCl, where Ti2AlN showed trans-passive behavior. Given that the corrosion behavior of (Ti,Nb)2AlC is unlike either Ti or Nb, the behavior of the former cannot be predicted from that of the latter.